This invention relates to a hollow fiber membrane fluid processing apparatus as exemplified by artificial hollow fiber membrane dialyzers for use with renal insufficient patients for removal of deleterious matters and water from blood and for adjustment of electrolyte and plasma separators.
A variety of hollow fiber membrane fluid processing apparatus were used in the past. Artificial hollow fiber membrane dialyzers are well known among others. In general, such a hollow fiber membrane dialyzer is of the structure comprising a cylindrical housing having inlet and outlet ports for dialyzing fluid and a fiber bundle in the form of a plurality of closely juxtaposed dialyzing hollow fiber membranes extending through the housing. The opposed ends of the fiber bundle are secured to the corresponding opposed ends of the housing by partitions in a fluid tight seal therewith, the partitions being formed by casting potting compound in place. Headers or caps are attached to the opposed ends of the housing outside the partitions to define inlet and outlet ports for blood. The commonly used dialyzing hollow fiber membranes are hydrophilic membranes, typically membranes of regenerated celluloses such as cellulose acetate and cuprammonium cellulose. Polyurethane is a typical potting compound. Plasma separators of a similar structure are also used.
FIGS. 6 and 7 show in enlarged cross section a portion of the partition surrounding the hollow fiber membranes in a typical prior art hollow fiber membrane dialyzer of the above-mentioned construction. FIG. 6 shows dialyzing hollow fiber membranes 22 in dry state, that is, prior to the actual use of the dialyzer. In this state, the dialyzing membranes 22 including their portion embedded in the partition 20 retain the as-fabricated shape, that is, have a substantially uniform inner diameter throughout the length.
On use, the dialyzer is primed by passing physiological saline through a flowpath, which is defined by the bore of the hollow fiber membranes and assigned for passage of blood, to replace the existing air by the saline before blood is passed through the dialyzer. A dialyzing fluid is admitted into another flowpath which is defined by the outside surface of the membranes and the housing inner wall. Then the dialyzing membranes 22 are wetted with water. The membranes 22 in wet state are shown in the enlarged cross section of FIG. 7. When water-containing fluid contacts the dialyzing membranes 22 which are hydrophilic, they absorb water and swell, resulting in an increase of their wall thickness. In the portion of the membranes 22 outside the partition 20, the increase of wall thickness appears as an increase of outer diameter while the inner diameter remains substantially unchanged. In the portion of the membranes 22 embedded in or in contact with the partition 20, the increase of wall thickness appears as a reduction of inner diameter because the partition 20 fixedly secures the membrane outer surface and prohibits any change of outer diameter. As a result, the membranes 22 narrow or reduce their inner diameter where they are in contact with the partition 20, the narrowed flowpath disturbing blood flow, thus leaving the risks of thrombus formation, clogging, and blood stagnation as well as an increased pressure loss across the dialyzer. Similar problems occur in plasma separators.